Founder Darian Shirazi, who started the company as Fwix a few years ago, was Facebook's first intern and worked for the social network for a year and a half.

So you'd think American Express would give his company a corporate card, right?

Not so, Shirazi told us. He had to personally guarantee the account to get a card.

American Express doesn't comment on individual clients, but this is a pretty common story we hear from startup founders. Because startups generally lack a financial history and lose money in their early years, it's hard for them to establish the kind of credit history that lenders like to see.

Still, surely they must have changed their mind after deciding to invest in Radius, right?

“We are impressed by Radius’ dedication to understanding what makes small businesses successful," American Express executive Harshul Sanghi said in a statement announcing the investment. "As Radius continues to build its comprehensive index of information on small businesses, we believe they offer a fantastic opportunity to efficiently understand the needs of the small business owner.”

Unless they need a business card, that is. Shirazi says he's still personally on the hook for to AmEx.

Update: We'd previously reported Radius as having 10 million customers; Shirazi tells us that number's not correct.